The present invention relates to communication systems, and more particularly, to a system and method for establishing a communication link between a wireless telephone and a base station transceiver subsystem (BTS).
Wireless communication devices, such as cellular telephones, rely on a network of cell sites located throughout a geographical-region to receive and transmit information. As shown in FIG. 1, a cellular telephone 10 is in communication with multiple cell sites 16 whenever the cellular telephone 10 is. powered on. Each cell site 16 includes a base station transceiver subsystem (BTS) 20 transmitting information to and receiving information from the cellular telephone 10 by using a cell site antenna 24. Multiple cell sites are strategically located throughout a geographical region so that cellular telephone coverage is consistent and continuous throughout the region. Groups of the cell sites 16 are connected to a base station controller (BSC) 30a, 30b by land lines 32 such that the cell sites 16 connected to the BSCs 30a, 30b will receive and transmit the same information. Although only two BSCs 30a, 30b are shown in FIG. 1, as many as 30 to 40 BSCs may be necessary to connect a sufficient number of the cell sites 16 together to provide adequate telephone coverage throughout a metropolitan region.
Upon powering up the cellular telephone 10, it transmits a number of operational parameters to one of the BSCs 30a, 30b to establish a communication link. The transmission from the cellular telephone 10 is received by one of the cell sites 16 in the vicinity, and the operational parameters are communicated via the associated BTS 20 to the BSCs 30a, 30b to which the particular cell site 16 and BTS 20 are connected. The BSCs 30a, 30b use the operational parameters to identify and register the cellular telephone 10 within its area of coverage. When the cellular telephone 10 is not currently being used to transmit or receive calls, the cellular telephone 10 remains in an idle state until there is a need to establish a communication link between the cellular telephone 10 and one of the BTSs 20.
The cellular telephone 10 and the cell sites 16 in the vicinity, use a frequency pair, known as a control channel 25 for signaling and exchanging operational parameters among them. Each cell site 16 contains a dedicated forward and reverse control channel. The reverse control channel is also called an access channel 27. Prior to receiving and transmitting information, as in a cellular call, a communication link between the cellular telephone 10 and one of the several cell sites 16 or BTSs 20 in the surrounding region must be established. Establishing such a communication link is facilitated by use of the control channel 25 and the access channel 27 on which the cellular phone 10 or the BTS 20 may exchange short messages. There is a paired control channel 25 and access channel 27 for each of the BTSs 20 within range of the cellular telephone 10. The information transmitted by the BTS 20 to the cellular phone 10 on the control channel 25 and by the cellular phone 10 to the BTS 20 on the access channel 27 provide the BTSs 20 with the necessary information to establish a communication link.
However, in the event the communication link fails to be established between the cellular telephone 10 and one of the BTSs 20, the incoming call will not be established, but will be aborted. Therefore, it can be appreciated that there is a need for a cellular telephone that increases the probability that a communication link will be established between the cellular phone and a BTS. The present invention provides this and other advantages, as will be apparent from the following detailed description and accompanying figures.
The present invention is embodied in a system and method directed to increase the likelihood that a communication link between a user station and a BTS is established, when an incoming message is to be received by the user station. In one embodiment, after receiving a paging message or incoming call, the system includes a user station that transmits a response message for a timeout period to a cell site or BTS, from which the user station received the paging message having the strongest signal strength, that is, to the primary BTS. In the event the primary BTS does not transmit an acknowledgment message to the user station before the timeout period expires, the user station then transmits the response message to that BTS from which the user station received the paging message having the second strongest signal strength on the respective control channel.
A BSC transmits the paging message to reach a cellular phone through sending simultaneous pages in multiple control channels (or paging channels) assigned to the BTSs. This invention will allow the cellular phone to establish communication with a second BTS, by using the control channel on which the paging message having the second strongest signal strength is received, when it fails the first time.
The user station includes a receiver to receive the paging message transmitted by multiple BTSs. The user station further includes a processor that analyzes and prioritizes the multiple BTSs into a sequence based upon the strength of the paging messages received. Coupled to the processor is a timer for timing the timeout period. The user station also includes a transmitter for transmitting the response message to one of the multiple BTSs in response to receiving the paging message.
In another embodiment of the present invention, the user station not only transmits the response message to the BTSs from which the user station receives the paging messages having the first and second strongest signals but will also transmit the response message to the BTS from which the user station receives the paging message having the next strongest signal when the timeout period has expired. The cellular telephone will continue transmitting the response message to each succeeding BTS in the sequence until the BTS to which the cellular telephone is currently transmitting responds with an acknowledgment message, or the number of BTSs to which the cellular phone may transmit is exhausted.